Recently, as disk-shaped storage media, optical disks have been put into practical use as large capacity data files and media for storing music or images. However, it further is intended to increase the capacities of such disk-shaped storage media so that they can be applied in more various uses. For efficient access to a large capacity optical disk, the following method is employed in general. That is, recording data are distributed to sectors in a certain unit of data size, and recording and reproduction are performed using the sectors as base units for rewriting. To the respective sectors as the base units for rewriting, addresses for identifying the sectors are added. Generally, the addresses are recorded as pits formed of concave and convex parts in an optical disk. A land/groove recording system has been employed commonly. In the system, track-guide grooves and inter-groove portions are used as areas for recording data in order to increase the density in a track direction.
A conventional optical disk having this sector configuration is described with reference to FIG. 12.
In FIG. 12(a), numeral 1001 indicates a substrate, numeral 1002 a recording film, numeral 1003 a first track, numeral 1004 a second track, numeral 1005 a sector of a divided portion of the track, numeral 1006 an address for identifying the sector, and numeral 1007 a data recording area for recording data. The first track 1003 is formed of a groove and the second track 1004 is formed of an inter-groove portion sandwiched by the groove of the first track. As shown in FIG. 12(a), the first track 1003 and the second track 1004 are configured to be positioned alternately on a one-revolution basis. Tracking by an optical beam is performed using the groove as a guide. However, the first track 1003 is in the groove and the second track 1004 is on the inter-groove portion, and therefore a tracking polarity is required to be inverted for the shift between the first track and the second track. As marks serving for detecting the polarity inversion, polarity inversion marks 1008 are provided in locations where the shift between the first track and the second track takes place. An optical disk device inverts the polarity in tracking using the polarity inversion marks 1008. In the sector 1005, the address 1006 and the data recording area 1007 are arranged as shown in FIG. 12(b).
Furthermore, as shown in FIG. 12(c), the address 1006 added for identifying the sector 1005 includes a sector mark 1009 indicating a sector starting point, a VFO mark 1010 used for generating a clock for the reproduction of the address part, an address mark 1011 for indicating the start of address data, a sector number 1012, a track number 1013, and an error detection code 1014. Since the sector mark 1009 and the address mark 1011 provide a data pattern for identifying the start of the address data, the data pattern is required to be a unique pattern that does not appear in the sector number 1012, the track number 1013, and the error detection code 1014. Therefore, the address data of the sector number 1012, the track number 1013, and the error detection code 1014 are recorded after being processed by bi-phase modulation or run-length-limiting modulation (RLL modulation). By this modulation process, a data pattern that does not appear from modulation rules for the other data can be obtained. Thus, a unique data pattern not in accordance with the modulation rules is used for the sector mark 1009 and the address mark 1011. The sector mark 1009 has a sufficient length to identify the start of the address area easily even when a PLL clock for synchronization is not locked.
As the modulation to the address data portion, the conventional example shown in FIG. 12 employs a bi-phase modulation in which “0” is modulated to be “00” or “11”, and “1” to be “10” or “01”. According to this modulation, a pattern with at least three “1” or “0” in a row is changed into a unique pattern not in accordance with the modulation rules. As the pattern not in accordance with the modulation rules, the conventional example shown in FIG. 12 employs “10001110” for the address mark 1011 and “111111110000000” for the sector mark 1009. A method of reproducing the address part in this conventional example is described briefly as follows.
Initially, the sector mark is detected. The sector mark has a unique pattern having eight “1” and eight “0” consecutively. When a mark with at least a certain length is detected using a free-running PLL clock, the sector mark 1009 can be detected easily. When this sector mark 1009 is detected, the PLL clock used for address demodulation is locked by the subsequent VFO 1010. After the lock of the PLL clock, the PLL clock determines “1” and “0” of the reproduced data, thus obtaining determination data. When the pattern of “10001110” as the address mark 1011 is detected from the determination data, the subsequent data are identified as the sector number 1012, the track number 1013, and the error detection code 1014. In this way, the detection of the address mark 1011 allows the subsequent data to be identified as the sector number 1012, the track number 1013, and the error detection code 1014 that are to be demodulated. Thus, the data are demodulated.
In the above-mentioned conventional example, the address part 1006 includes the VFO mark 1010 for clock synchronization. However, a method in which the clock for demodulating address data is obtained by another means also has been practiced. This type of conventional example is described with reference to FIG. 13.
In FIG. 13(a), numeral 1101 indicates a substrate, numeral 1102 a recording film, numeral 1103 a track, numeral 1104 a sector of a divided portion of the track, numeral 1105 a segment of a divided portion of the sector, numeral 1106 an address for identifying the sector, and numeral 1107 a data recording area for recording data.
As shown in FIG. 13(b), in the leading location of the segment 1105, wobble pits 1108 used for obtaining a tracking signal and the subsequent clock pit 1109 for generating a clock for address and data demodulation are provided. As shown in FIG. 13(c), the address 1106 added to identify the sector 1104 includes an address mark 1110 for indicating the start of the address data, a sector number 1111, a track number 1112, and an error detection code 1113. As in the above-mentioned conventional example, the address mark 1110 has a unique pattern that does not appear in the sector number 1111, the track number 1112, and the error detection code 1113. Similarly in the conventional example shown in FIG. 13, the bi-phase modulation is employed for modulating the address data portion and “10001110” is used as the address mark 1110 as in the above-mentioned conventional example.
A method of reproducing the address part in this conventional example is described briefly as follows. Initially, the clock pit 1109 is detected. Using this clock pit, the frequency of a clock pit detection signal is multiplied by N using the PLL, thus generating a PLL clock for address demodulation. In the trailing part of the PLL clock, as in the above-mentioned conventional example, “1” and “0” of the reproduced data are determined, thus obtaining determination data. When the pattern of “10001110” as the address mark 1110 is detected from this determination data, the subsequent data are identified as the sector number 1111, the track number 1112, and the error detection code 1113. In this way, the detection of the address mark 1110 allows the subsequent data to be identified as the sector number 1111, the track number 1112, and the error detection code 1113 that are to be demodulated. Thus, the data are demodulated.
In a conventional optical disk, however, a unique pattern that does not appear in an address data portion has been required as an address mark to identify the starting position of an address. Therefore, recording was performed after the process of the data portion of the address by the bi-phase or RLL modulation. In a 1–7 modulation or 2–7 modulation as a type of bi-phase modulation or RLL modulation, one bit of address data becomes two bits or 1.5 bits after the modulation, thus increasing redundancy. Therefore, there has been a problem that the area required for the address data portion increases and thus the data recording area is reduced.
Moreover, in a conventional magneto-optical disk, in order to reproduce the first track and the second track continuously, a detection pit for tracking polarity inversion is provided, which also has been a factor that reduces the area in or from which data are recorded or reproduced. Furthermore, in the case of using one bit of the polarity inversion detection pit, it has been difficult to secure sufficient reliability with respect to defects of the disk and damages on the disk surface.